Unify the configuration of the compiler docs

Previously it was rather inconsistent which crates got the rust logo and
which didn't and setting html_root_url was forgotten in many cases.

src/lib.rs

diff --git a/src/lib.rs b/src/lib.rs
index 9f5b03c..c3fa570 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,9 +13,6 @@
  * TODO(antoyo): remove the patches.
  */
 
-#![allow(internal_features)]
-#![doc(rust_logo)]
-#![feature(rustdoc_internals)]
 #![feature(rustc_private)]
 #![recursion_limit = "256"]
 #![warn(rust_2018_idioms)]